Organic light emitting devices (OLEDs) are a new generation of display technology. As depicted in FIG. 1, a typical OLED 100 includes a layer of indium tin oxide (ITO) as an anode 102, a single layer of hole-transporting materials (HTL) 104, a single layer of emissive materials (EML) 106 including emitter and host, a single layer of electron-transporting materials (ETL) 108 and a layer of metal cathode 110. The emission color of OLED is determined by the emission energy (optical energy gap) of emitters. Phosphorescent OLEDs (i.e., with phosphorescent materials as emitters) have higher device efficiency that fluorescent OLEDs (i.e., with fluorescent materials as emitters).
The development of efficient blue OLEDs is important for applications in displays, backlighting for displays and solid state lighting. The reported blue phosphorescent OLEDs use cyclometalated iridium complexes as emitters. These emitters require the supply of iridium, which is present in low abundance (3×10−6 ppm) in the Earth's crust.